Aquarium filter systems which continuously circulate water from an aquarium, through a filter medium and, then, back to the aquarium are well known in the art. One such type of aquarium filter system is represented by the external-type system which employs a small container comprising a filter mounted on the side of the aquarium. The water from the aquarium is drawn by means of a water pump, it flows through filter medium in the container and is then returned to the aquarium. The filter medium is usually in the form of elements of activated carbon or charcoal and fluffy masses of synthetic resin fibers.
Examples of external-type filter systems can be found in U.S. Pat. Nos. 3,513,978 to Newsteder and 3,525,435 to Conner, both of which are herein incorporated by reference in their entirety.
The Newsteder system uses two separate compartments, each filled with a different filtering substance (i.e., fibrous filtering material and charcoal respectively). The water flows through the fibrous material and then through the charcoal before going back to the aquarium. In this type of filter, however, the compartment holding the charcoal must have very restricted openings to prevent any charcoal from passing through openings into the aquarium.
The Conner filter uses a perforated top with a dependent filter bag that is filled with charcoal. The flow of the water is down through the top, out through the bag walls and then back into the tank. The Conner filter is wholly disposable. The filter, however, lacks a mechanism for mechanically or physically filtering water prior to passing through the charcoal. Consequently, the filter allows waste particles to enter the interior space of the filter and, thereby, reduce the effectiveness of the charcoal. Specifically, particulate matter can block (or occlude) the surface of adsorbents like charcoal and activated carbon and, thus, reduce their capacity to surface adsorb dissolved gases and toxins.
Another type of aquarium filter is the internal or underwater filter. A container is provided which includes a filter medium such as activated carbon or charcoal and a fluffy mass of synthetic resin fibers. An air lift is provided, extending vertically up from the container, and air is pumped down into the base of the air lift from an external air pump. The air rises which, in turn, induces water flow into the container, such that the water passes through the filter medium and, then returns back to the aquarium.
In aquarium filtration, the filter medium provides various types of filtration activity. As the water flows through a porous wall, mechanical filtration of the water occurs with the walls acting as a sieve, retaining the solid contaminants. The mechanical filtering capability of this “sieve-type” mechanism increases for finer contaminants as the surface area of the porous wall increases and the pore size of the openings or interstices decrease. Increasing the density of the porous wall results in improved trapping of smaller particles. Such increases in the surface area of the porous wall, however, also results in accelerated clogging rates of the porous wall. Therefore, a need exists for filter cartridges providing mechanical filtration using high density (or, high surface area) porous walls to improve the filtration of finer contaminants without a corresponding acceleration in the clogging rate of the filter cartridge as a whole.
The present inventors have discovered that filter cartridges incorporating dual density filters, comprising a low-density (surface area) in-flow porous wall and a high-density (surface area) out-flow porous wall, provide improved mechanical filtration without accelerating clogging.
Accordingly one aspect of the present invention is to provide improved filter cartridges.
A further aspect of the present invention is to provide filter cartridges which improve mechanical filtration without accelerating the clogging of the filter cartridge.
A still further aspect of the present invention is to provide filter cartridges comprising a plurality of filter walls produced from porous materials, with each wall varying in density or surface area such that the density or surface area of the filter walls increases in the direction of water flow.
These and other advantages are accomplished by the present invention as will be further detailed in the following description.